Solar cells are semiconductor devices that convert sunlight into electricity. Typically, solar cells are replicated over an area and interconnected in series and in parallel to form solar cell arrays. These arrays are distributed over a surface and encased in an enclosure to form a solar cell panel. Solar cells are used as sources of electricity for both terrestrial and space applications. The key challenge in making terrestrial solar cells into a widespread source of electricity that is competitive with more conventional forms of electrical generation is in lowering the manufacturing cost.
An area in which the manufacturing cost of terrestrial solar cells requires reduction is that of the interconnection of the solar cells. For crystalline silicon solar cells, a common method for interconnecting solar cells involves the use of "over-andunder" contacts of a generally Z-shaped configuration. These contacts connect the back side of one solar cell to the front side of an adjacent solar cell. This procedure requires being able to access first the front of one solar cell and then the back of the adjacent cell. The result is a slow, expensive manufacturing step with high capital costs and high labor costs.
An alternative to the Z-shaped configuration is a wraparound contact. A wraparound contact includes a front contact which is wrapped around the edges of the solar cell making it accessible from the back of the cell along with the back contact. Wraparound contacts have the potential for significant cost reduction and avoid the foregoing disadvantages of known interconnection procedures. Furthermore, using a wraparound approach, the individual solar cells may be packed more densely. Increased packing density is advantageous since a greater proportion of the solar panel surface is available to collect sunlight. This provides increased energy output per unit surface area of solar panel, a result generally desirable for all solar cell applications.
The formation of a wraparound metal contact has been implemented through various techniques. One method involves photolithographic deposition of a metal directly onto the surface of a solar cell by sputtering or vacuum evaporation. Another method, for forming a version of wraparound contacts termed "wrap-through" contacts, uses a laser to form holes or channels so that the front contact can be brought to the back side of the solar cell. Yet another method is screen printing of a conductive metal-glass paste directly onto the surface of a solar cell. See, for example, U.S. Pat. Nos. 4,135,290; 4,361,950; 4,897,123; and 5,425,816 for disclosure of methods for fabricating wraparound contacts on solar cells.
The aforementioned wraparound methods for solar cells tend to be costly, slow, and not readily adaptable to automation. As a consequence, none of these methods satisfy the need for a low cost manufacturing method for wraparound contacts for terrestrial solar cells.